In this book, I have optimized the growth of n- and p-GaN films, and high quality InGaN/GaN multiple quantum wells (MQWs) on sapphire (0001) substrate by a low pressure metal-organic chemical vapour deposition and have fabricated high brightness InGaN/GaN MQW light-emitting diodes (LEDs) under optimum conditions. To improve quantum efficiency which is generally poor in the conventional rectangular-shaped QWs due to spatial indirect recombination induced by internal piezoelectric field, we proposed a possibility of quantum dot (QD) engineering with triangular-shaped band structure in the InGaN/GaN QWs. The structural and optical properties of the InGaN/GaN MQWs with different threading dislocation densities were also investigated. The effects of Si-doped n-GaN and Mg-doped p-GaN layers on the electrical and optical properties of the InGaN/GaN MQW LEDs were investigated and optimized under various growth parameters.